JP7189432B2 - optical signal processor - Google Patents

Description

The present invention relates to an optical signal processing device, and more particularly to an optical signal processing device having an optical switch function.

2. Description of the Related Art Conventionally, in optical communication networks, an optical transmission communication system called CDC (Color-less, Direction-less, Contention-less)-ROADM (Reconfigurable Optical Add/Drop Multiplexer) has been introduced. In the CDC-ROADM network node, a MultiCast Switch (MCS) directs the transponders accommodated in the node to any direction (Color-less) without depending on the wavelength of the signal light (Direction- less) An optical input/output device that serves as a key device that enables contention-less connection of optical signals of the same wavelength assigned to different paths within an optical node.

Miniaturization of the MCS is required for efficiency improvement of the optical transmission device. So far, a compact MCS that uses a PLC (Planar Lightwave Circuit) and adopts a configuration called PILOSS (Path-Independent Insertion-Loss) has been reported. (See Non-Patent Documents 1 and 2 below)

Mach-Zehnder Interferometer (MZI) switches (Non-Patent Document 3) are often used as switch elements in the MCS and PILOSS switches as described above.

FIG. 1(a) is a diagram showing an MZI switch, which is an element functioning as a switch element composed of optical waveguides. In the MZI switch shown in FIG. 1( a ), an optical signal input from one of the two optical waveguides on the left end is branched into two upper and lower optical waveguides (arms) at the left directional coupler. A phase change is given by a phase shifter formed in at least one of the optical waveguides, and as a result of recombining and interfering in the directional coupler on the right side, one of the two optical waveguides on the right end is switched according to the phase change ( switching) is output.

FIG. 1B is a diagram showing an optical signal processing device (switch) configured by connecting a plurality of switch elements such as MCS switches and PILOSS switches in multiple stages. As shown in FIG. 1(b), by using a plurality of MCS switches and PILOSS switches as switch elements and connecting them in a plurality of stages in the z-axis direction, the extinction ratio of the switches can be increased. In this case, the number of MZI switches required to construct the same size switch doubles.

T. Watanabe, et. al. , “Silica-based PLC Transponder Aggregateors for Colorless, Directionless, and Contentionless ROADM”, OFC/NFOEC2012, OTh3D. 1, March 8, 2012, Los Angeles Takashi Goh, Akira Himeno, Masayuki Okuno, Hiroshi Takahashi, and Kuninori Hattori, "High-Extinction Ratio and Low-Loss Silica-Based 8x8 Strictly Nonblocking Thermooptic Matrix Switch", J. Lightwave Technology. VOL-17, NO. 7, p-p 1192-1199, JULY 1999 T. Shibata et al. , "Silica-based waveguide-type 16 x 16 optical switch module incorporating driving circuits," in IEEE Photonics Technology Letters, vol. 15, no. 9, pp. 1300-1302, Sept. 2003.

FIG. 2 shows a plan view of the basic structure of a conventional optical signal processing device. In this specification, the z-axis is the direction of the entire light waveguide, the y-axis is the direction of the row of switch elements by MZI, and the yz plane corresponds to the substrate plane of the PLC (planar optical circuit). ing.

The optical signal processing device shown in FIG. 2 has four MZI switches, which are switch elements, on the left input side and four MZI switches, which are switch elements, on the right output side. In this configuration, an MZI switch, which is a switching element, is also arranged between the MZI switch on the side and the MZI switches are connected by an optical waveguide. Four stages of MZI switches are connected in each column in the y-axis direction. In FIG. 2, in addition to the optical waveguide connecting the output of the MZI switch in the front stage of each row and the input of the MZI switch in the rear stage, the second row in the y-axis direction among the MZIs arranged on the yz plane is shown. It includes an optical waveguide formed between a row of MZI switches connected in three stages and a row of MZI switches connected in three stages in the third row.

However, in the configuration of the conventional optical signal processing device shown in FIG. You will need to get close. It is known that when optical waveguides are close to each other, coupling of propagation modes occurs and an optical signal is transferred from one optical waveguide to the other optical waveguide. Therefore, if the interval between the switch elements is narrowed, optical signal leakage (crosstalk) occurs between the optical signals, degrading the signal characteristics of the optical signals.

In order to avoid this, it is necessary to ensure a sufficiently wide interval between the switch elements, resulting in the problem of increasing the chip size of the PLC.

SUMMARY OF THE INVENTION The present invention has been made in view of such problems, and an object of the present invention is to provide an optical signal processing apparatus in which the distance between switch elements is narrowed to reduce the size and crosstalk is reduced. It is in.

To achieve these objectives, an aspect of the invention is an optical signal processing apparatus. An optical signal processing device according to one embodiment includes a plurality of input optical waveguides, a plurality of output optical waveguides, a plurality of optical waveguide elements arranged between the plurality of input optical waveguides and the plurality of output optical waveguides, A connection optical waveguide, wherein the width and propagation constant of the connection optical waveguide adjacent to the optical waveguide element are different from the width and propagation constant of the optical waveguide constituting the adjacent optical waveguide element, and are adjacent to the optical waveguide element. The width of the connecting optical waveguide is configured to be wider than the width of the optical waveguides forming the adjacent optical waveguide element .

As described above, according to the present invention, it is possible to realize an optical signal processing device in which crosstalk is reduced while narrowing the distance between switch elements.

(a) shows a switch element (MZI switch) configured by an optical waveguide, and (b) shows an optical signal processing device (switch) configured by connecting a plurality of switch elements. FIG. 2 is a diagram showing an optical signal processing device (switch) configured by arranging a plurality of switch elements in the y-axis and z-axis directions and connecting the outputs and inputs of the switch elements; 3A is a diagram showing the configuration of the optical signal processing apparatus of the first embodiment, and FIG. 3B is a part of FIG. is an enlarged view of a region where optical waveguides that are not connected are adjacent to each other; FIG. 10 is a diagram showing the configuration of an optical signal processing device according to a second embodiment; FIG. 11 is a diagram showing the configuration of an optical signal processing device according to a third embodiment;

The basic idea of the present invention can be said to be, for example, the following (i)-(iii).

(i) The multi-input multi-output optical switch of the PILOSS configuration has a configuration in which the output of the switch element in the preceding stage and the input of the switch element in the subsequent stage among the switch elements connected in multiple stages are connected.

(ii) When connecting switch elements skipping a specific stage switch element, it is necessary to pass an optical waveguide between the switch elements. (For example, when connecting the output of the n-th switch element and the input of the (n+2)th switch element among the switch elements arranged in multiple stages in p columns, the n+1th switch element is skipped. It is necessary to form and connect an optical waveguide between the n+1th switch element in the pth column and the n+1th switch element in the p+1th column (or p−1th column).)

(iii) by making the propagation constant of the optical waveguides formed between the switch elements in (ii) different from the propagation constant of the optical waveguides forming the switch elements, the optical waveguides forming the switch elements and the switch elements It is possible to suppress crosstalk (TX) of optical signals that may occur with an optical waveguide formed therebetween.

By configuring the optical signal processing device so as to satisfy the above, it is possible to narrow the interval between the switch elements while ensuring low crosstalk characteristics.

Since the switch element is usually composed of an element mainly composed of an optical waveguide such as an MZI (FIG. 1(a)), it will be referred to as an optical waveguide element in the following description.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings of the following embodiments, the left end of the optical signal processing device is assumed to be the input side, and the right end thereof is the output side. , the right end may be the input side, and the left end may be the output side. Further, the optical signal processing device may have a multi-stage configuration, and the optical waveguide on the output side of the optical waveguide element in each stage may be connected to the optical waveguide on the input side of the optical waveguide element in the next stage. Alternatively, the optical waveguide element on the output side of the previous stage may be the optical waveguide element on the input side of the subsequent stage.

(Example 1)
FIG. 3(a) shows a plan view of the connecting optical waveguides and switch elements of the optical signal processing device according to the first embodiment of the present invention.

FIG. 3(a) shows an optical signal processing device having a total of 8 optical waveguide elements, 4 on the left input side and 4 on the right output side, as in the conventional example of FIG. 1, for simplicity. . Further eight optical waveguide elements are arranged between the four optical waveguide elements on the input side and the four optical waveguide elements on the output side. A total of 16 optical waveguide elements are arranged in 4 rows and 4 columns in the yz plane. The optical waveguide elements on the input side and the output side are connected by two sets of four connecting optical waveguides. Also, in FIG. 3(a), optical waveguides that are not connected to the 16 switch elements shown are arranged from left to right between the switch elements (the switch element arranged in the second row in the y-axis direction and the third row). between the switch elements arranged in the eye). As described above, if the distance between the optical waveguide elements in the y-axis direction is narrow, the propagation modes of the optical waveguides are coupled, and crosstalk occurs between the optical waveguides.

FIG. 3(b) is a diagram showing optical waveguides formed between switch elements in the third row (third from the left) of the second and third rows in the y-axis direction in FIG. 3(a). FIG. 3B shows switch elements in the second row (second from the left) in the second row and third row in the y-axis direction in FIG. FIG. 10 is an enlarged view of an area where optical waveguides (or optical waveguides constituting switch elements) connecting the first (fourth) switch element and optical waveguides not connected to the illustrated switch element are adjacent to each other.

The coupling strength of the propagation modes of the adjacent optical waveguides becomes stronger as the distance between the optical waveguides becomes shorter, even if the adjacent distance is short. Therefore, if the optical waveguides are too close, crosstalk of optical signals will occur. Also, this coupling strength is maximized when the propagation constants of the two are the same, and becomes small when the propagation constants of the two are different.

The propagation constant of the optical waveguide changes depending on the refractive index difference between the core and the clad, the refractive index distribution, and the shape of the core. When an optical signal processing device is formed by optical waveguides on a single chip, the refractive indices of the core and cladding are usually determined at the time of fabrication, but it is possible to control the propagation constant by adjusting the shape of the adjacent optical waveguides. is. In particular, the thickness of the optical waveguide can be controlled by an exposure mask when forming the core, and can be easily changed.

In this embodiment, as shown in FIG. 3(b), by changing the thickness of the adjacent optical waveguides, the propagation constants of both are changed, and the coupling of the propagation modes between them and the resulting crosstalk can be suppressed. In FIG. 3B, the thickness (width in the y-axis direction) of the center optical waveguide among the three adjacent optical waveguides is made larger than the thickness of the other two optical waveguides. Two optical waveguides other than the central optical waveguide in FIG. When adjacent to the constituent optical waveguides, the propagation constants of the other two optical waveguides other than the central optical waveguide in FIG. , may be different from the propagation constant of the optical waveguide that constitutes the switch element of FIG. 3(a).

For example, when the distance (distance in the y-axis direction) between adjacent optical waveguides is 40 μm, two optical waveguides are arranged so that the ratio of the thickness (width in the y-axis direction) of the two optical waveguides is 1.03 times. , the crosstalk can be suppressed by making the propagation coefficients of both different.

In the above examples, an optical waveguide with both ends connected to a switch element may be replaced by an optical waveguide with at least one end connected to a switch element, and/or an optical waveguide with both ends not connected to a switch element. , at least one end of which is not connected to the switch element. Alternatively, in the above example, either the optical waveguide whose both ends are connected to the switch element or the optical waveguide whose both ends are not connected to the switch element may be omitted. In this case, the propagation constants of the optical waveguides having at least one end connected to the switch element may be different from the propagation constants of the optical waveguides forming the switch elements arranged close to each other in the y-axis direction. Alternatively, the propagation constants of the optical waveguides having at least one end connected to the switch element may be different from the propagation constants of the optical waveguides forming the switch elements arranged close to each other in the y-axis direction.

Further, in the above example, there are no optical waveguides whose both ends are connected to switch elements and optical waveguides whose both ends are not connected to switch elements. may have different propagation constants of the optical waveguides constituting the .

(Example 2)
FIG. 4 is a diagram simply showing the configuration of an optical signal processing apparatus according to Embodiment 2 of the present invention. The optical signal processing device of this embodiment is a 4-input 3-output PILOSS switch, and connects input and output optical waveguides, switch elements which are MZI switches arranged two-dimensionally in the yz plane, and switch elements. and a connecting optical waveguide. In such a PILOSS switch with asymmetric input and output, there is a connecting optical waveguide that skips each stage of the switch elements arranged in multiple stages and connects to the switch element of the next stage.

As described above, the overall size of the switch can be reduced by placing the switch elements as close together as possible. However, if the distance between the switch elements in the y-axis direction is too small, the propagation mode between the connection optical waveguide formed between the switch elements and the optical waveguides constituting the switch elements (constituting the MZI switch) will Crosstalk between the coupling and the optical signal will occur.

On the other hand, by making the thickness of the connecting optical waveguide formed between the switch elements different from the thickness of the optical waveguides constituting the switch elements, the propagation constant between the two changes, and the propagation mode coupling is weakened. Crosstalk of optical signals can be suppressed. Therefore, the distance between the optical waveguides in the optical signal processing device can be reduced, and the size of the chip can be reduced.

In addition, not only the optical waveguide formed between the MZI switches to skip the MZI switches at each stage, but also the propagation constant of the optical waveguide constituting the MZI switch in the adjacent MZI switch is changed, so that the MZI switch It is also possible to suppress crosstalk of optical signals between them. This can be achieved by employing different width optical waveguides in adjacent MZI switches.

(Example 3)
FIG. 5 is a diagram simply showing the configuration of an optical signal processing apparatus according to a third embodiment of the present invention. The optical signal processing device of this embodiment is a multicast switch (MCS) employing a 4-input 3-output PILOSS configuration, and is an MZI switch two-dimensionally arranged on the yz plane with input and output optical waveguides. It includes an element, a connecting optical waveguide connecting between the switching elements, and an optical splitter. In a switch adopting such a PILOSS configuration in which the input and output are asymmetrical, each stage of switch elements arranged in multiple stages is skipped, and a connection optical waveguide connecting to the switch element of the next stage is provided as in the second embodiment. exist. Therefore, as in the second embodiment, by making the thickness of the connecting optical waveguide formed between the switch elements different from the thickness of the optical waveguides constituting the switch elements, the propagation constants of the two change, resulting in propagation mode coupling. can suppress the crosstalk of the optical signal. Furthermore, not only the optical waveguides formed between the MZI switches to skip the MZI switches at each stage, but also the propagation constants of the optical waveguides forming the MZI switches in the adjacent MZI switches are changed, so that the MZI switches It is also possible to suppress crosstalk of optical signals between them.

Claims (6)

An optical signal comprising a plurality of input optical waveguides, a plurality of output optical waveguides, a plurality of optical waveguide elements arranged between the plurality of input optical waveguides and the plurality of output optical waveguides, and a connecting optical waveguide. A processing device,
The width and propagation constant of the connection optical waveguide adjacent to the optical waveguide element are different from the width and propagation constant of the optical waveguide constituting the adjacent optical waveguide element,
An optical signal processing device , wherein the width of the connection optical waveguide adjacent to the optical waveguide element is wider than the width of the optical waveguide forming the adjacent optical waveguide element . The connection optical waveguide includes a first connection optical waveguide having at least one end connected to the optical waveguide element, and the propagation constant of the first connection optical waveguide constitutes the adjacent optical waveguide element. 2. The optical signal processing apparatus of claim 1, wherein the propagation constant of is different from that of . The connection optical waveguide includes a second connection optical waveguide at least one end of which is not connected to the optical waveguide element,
The propagation constant of the second connecting optical waveguide is different from the propagation constant of the optical waveguides forming the adjacent optical waveguide elements, or
3. The optical signal processing device according to claim 1, wherein the propagation constant of said second connecting optical waveguide is different from the propagation constant of said first connecting optical waveguide having at least one end connected to said optical waveguide element. 4. The optical signal processing device according to claim 1 , wherein said optical waveguide device comprises a Mach-Zehnder interferometer. 5. The plurality of optical waveguide elements according to any one of claims 1 to 4 , forming a multiple-input multiple-output optical switch in which a PIOSS structure in which optical waveguide elements are arranged in multiple stages is arranged in a direction orthogonal to an optical waveguide direction. optical signal processor. 6. The optical signal processing device according to claim 5 , wherein said multiple-input multiple-output optical switch has a function of a multicast switch.

Images